Grate structure for incinerator

ABSTRACT

In a hollow pyrometric incinerator grate structure are groups of axially spaced grate support means such as rings. Elongated grate bars are disposed on the support means circumferentially in rows about the interior of the hollow body. Each grate bar is engaged at its center with an intermediate support and the opposite ends of each grate bar bear freely on opposite axially spaced supports to enable biaxial stress relief.

United States Patent 1191 Schrage Jan. 8, 1974 [54] GRATE STRUCTURE FORINCINERATOR 1,575,350 3/1926 McEwen 110/35 1 Inventor: Donald sci-rage,Germanwwn, 5352122 111323 1 113 37311111: 13:13:11..116132 3,577,9415/1971 Schoppe Q 110/14 [73] Assignee: Aqua-Chem, Inc., Milwaukee, Wis.

Primary Examiner-Kenneth W. Sprague [22] Flled' 1972 Attorney-Ralph G.Hohenfeldt et al. [21] Appl. No.: 247,579

[57] ABSTRACT ((51. 110/ 11:2,; In a hollow pyrometric incinerator grateStructure are Fieid 4 35 groups of axially spaced grate support meanssuch as 1 7 rings. Elongated grate bars are disposed on the supportmeans circumfere'ntially in rows about the inter- 56] References Cited101' of the hollow body. Each grate bar is engaged at its center with anintermediate support and the opposite UNITED STATES PATENTS ends of eachgrate bar bear freely on opposite axially 3,487,793 1/1970 Lerner et a1.110/14 s a ed supports to enable biaxial stress relief. 2,426,348 8/1947Fulton et a]. 110/35 2,116,024 5/1938 Helmick 126/167 X 14 Claims, 9Drawing Figures E1 A 1&1 r 32 a 22 e\\ Q 1 e 11 23 -r I 1y I 135 l 34 lll 59 I 28 1t 7' I i Er Q 1 j 27 2O 2 H w PATENTEU 8*974 3,783,802

SHEET 1 BF 2 PMENTED JAN 81974 SHEET 2 BF 2 r 1 GRATE STRUCTURE FORINCINERATOR BACKGROUND OF THE INVENTION This invention relates toincinerators, and, in particular, to improvements in the rotatingpyrometric cone or grate structure used in incinerators for combustiblewaste materials such as garbage.

A known type of incinerator has an open-ended hollow body or gratesupport structure which is sometimes conically shaped and is mountedwithin an enclosure on an inclined axis of rotation. Disposed circularlyaround the interior of the hollow body are rows of grate bars on whichthe combustible materials are deposited. The combustible materials areignited initially with a gas flame or the like while the body isrotating slowly. Ignition is sustained by forcing air for combustionfrom the outside to the inside of the body through the grates.

The prevailing combustion temperatures are sufficient to cause thegrates and the hollow supporting body to become more than red hot.Alternate heating and cooling and uneven thermal distribution in thebody and grates causes internalstresses, distortion and other forms ofdeterioration which have necessitated premature replacement orrebuilding of thegrate structure.

Fastening the grate bars in the hollow conical body has presentedproblems. It has been the custom to hold the grates within the hollowgrate support body by means of several slots in the edge of each gratebar which hook onto axially spaced apart rings within the body. When thegrate bars are alternately subjected to cooling and heating, expansiveand contractive thermal stresses are developed in them. These stressesoften result in the grate bars fracturing in the vicinity of theirsupport engaging slots in which case some of the bars may break awaycompletely with obvious undesirable consequences. Moreover, when one ormore grate bars breakaway, the self-supporting effect of adjacent barsis removed in which case there is a greatertendency for the remainingbars to twist, fracture and shear off.

The hollow supporting body for the grates has also presented problems.The body is desirably supported in cantilever fashion to allow an openend for charging its interior with burnable materials, but this makesthe conical grate structure particularly vulnerable to distortion andfracture due to cyclical and uneven thermal distribution.

' SUMMARY or THE INVENTION An object of the present invention is toovercome the abovenoted disadvantages by providing a grate structurewhich is capable of adapting to varying thermalstresses withoutdistorting or fracturing.

Another important object of this invention is to provide means forsupporting the grates within the structure in such manner that thegrates are not subjected to undue tensil, compressive, shearing ortorsional stresses.

Another object is to have only a central region of each grate engagedwith an intermediate support in the support structure and to have theend portion of the grates merely bearing on their supports so that theyare free to expand and contract without developing high internalstresses.

A further object is to provide a conical grate support structure whichis constructed as a lattice so as to accommodate thermal changes withoutfracturing.

How the foregoing and other more specific objects of the invention areachieved will appear throughout the course of a more detaileddescription of a preferred embodiment of the invention which will be setforth hereinafter.

In general terms, one embodiment of the new grate structure comprises ahollow cone which is formed of generally axially directed struts thatengage with axially spaced apart flange rings. The struts areinterconnected with each other to form what may be termed a latticestructure. This structure accommodates axially and circumferentiallyimposed thermal stresses.

The axially adjacent rows of grates which are disposed about theinterior of the support structure each have a central slot on one edgeor some other suitable means for relatively loosely engaging the grateswith sets of intermediate rings that encircle the interior of the hollowbody. Axially spaced apart in opposite directions from each intermediatering are supporting rings on which the opposite end portions of eachgrate bear. There is no positive engagement between the end portions ofthe grates and their supporting rings.

An embodiment of the invention will now be described in reference to thedrawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial vertical sectional viewof an incinerator which employs the new grate structure;

FIG. 2 is a partial sectional view taken on an axial plane through thegrate structure;

FIG. 3 is a side elevation view of the grate structure with one halfshowing the exterior thereof and the other half showing the interiorwith the grates removed;

FIG. 4 is a semi-plan view looking at the plane 44 in FIG. 3, onequadrant showing the circularlydisposed grate supporting ring means andthe other having the same omitted to show the outside struts of thegrate supporting body;

FIG. 5 is a fragmentary elevation view of the joints between the strutsand other members of the hollow FIG. 6 is a side elevation view of oneform of elongated gate which may be used in the new incinerator gratestructure;

FIG. 7 is a bottom-edge view of the grate in FIG. 6;

FIG. 8 is a side elevation view of another form of elongated grate thatmay be used in the new grate structure; and

FIG. 9 is a plan view of the grate shown in the preceding figure.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 shows an incinerator with aportion of its housing 10 broken away to expose the inclined conicalpyrometric cone or grate structure 11 constituting the subject of thepresent invention. More information on an incinerator of this type maybe obtained from US. Pat. No. 3,577,941 which is assigned to theassignee of the present invention.

The invention is directed to improving the hollow generally conical body11 and the means for supporting a multiplicity of interiorly arrangedrows of grates 12 therein. Body 11 is supported for rotation on aturntable 13 about an axis that is inclined from horizontal. Thestructural details of the body 11 will be discussed later. For presentpurposes it is sufficient to observe that the body 11 has an open end 14through which combustible material can be fed to the interior for beingburned. The feed end 14 is provided with a beveled annular metal shroud15. The shourd l5 helps to retain combustible materials in body 11 whenit is being rotated during combustion.

Hollow body 11 has a flange ring 16 at its lower end. Although it is notevident in FIG. 1, flange ring 16 has an aperture which is in alignmentwith an aperture in turntable 13 so that large unburnable residues maybe discharged from the hollow body 11 periodically. Also not visible inthe drawing but exemplified in the cited patent is a convex valve memberwhich is adapted to be selectively positioned in the aperture ofturntable 13 to close it when the incinerator is in use. A lead screw,not shown, which is driven by a shaft 17 on whose end there is ahandwheel 18 may be used to advance and retract the convex valve memberinto and out of the aperture in turntable 13. There is a turntable basestructure 19 which is surrounded by several circumferentially spacedrollers 20. Behind or below base structure 19 is a housing 21 in whichthere is a suitable shaft for supporting the hollow body 11 for rotationand a reduction gear train which, like the shaft, is not shown. On topof housing 21 there is a speed reducer 22 which is connected to a primemover such as a motor that is located behind the speed reducer and notvisible in FIG. 1. A shaft 23 extends from speed reducer 22 into a gearhousing 24. There is a pinion on the end of shaft 23 which engages witha large gear within housing 24, the pinion and gear not being shown, butit will be understood that they constitute part of the known mechanismfor rotating the hollow body 11 at rotational speeds under onerevolution per minute.

Hollow body 11 and its supporting and driving structure which was justdescribed are all mounted on a car-' riage which is marked with thenumeral 25. The carriage 25 has four wheels two of which, 26 and 27, arevisible in FIG. I. The wheels run on parallel tracks such as the onemarked 28. These tracks lay on opposite sides of the incineratorenclosure so that the sides of carriage remain on the outside of theenclosure when the hollow body 11 is in place within it.

The roof 29, front wall 30 and rear wall 31 together with the side wallswhich are not shown, are all refractory lined to cope with the intenseheat that develops in enclosure 10 during incineration. Rear wall 31 hasa vertical portion as shown and a refractory lined inclined portion 32which connects with and is supported on base 19 and carriage 25. Thus,the construction is such that when carriage 25 is rolled to the right ontracks 28 as in FIG. 1, the body 11 and its associated parts will beexposed for maintenance and there will also be access to the interior ofenclosure 10 for maintenance purposes.

When the interior of hollow body 11 is charged with wastes, the wastesmust be ignited initially by external means. Thus, a gas jet 33 isprovided for directing a flame into hollow body 11 to effect ignition.The flame may also be continued during regular operation of theincinerator to assist combustion of evolved gases and solid materials.When combustion of waste has commenced in hollow body 11, the combustionprocess is promoted and sustained by blowing air from the outside of theinside of body 11 through suitable grooves in the sides of grates 12.The combustion air injection means is symbolized by a header 34 whichmay have several jet openings or nozzles in its top for projecting airat relatively high velocity through the grate openings and into hollowbody 11. There may be several air jet headers 34 adjacent each other andthey may each be connected to a blower, not shown, by means of pipessuch as the one marked 35. Fine ashes which are produced by combustionof the wastes fall through the spaces or grooves between grates 12 andsettle into an ash hopper, not shown.

The gaseous products of combustion which may be incompletely oxidized inhollow body 1 l are withdrawn upwardly through the inlet of anafterburner 36, a fragment of which is shown in FIG. 1. The duct whichextends into enclosure 10 for directing gases to the afterburner isomitted from the drawing. There is also a conduit or chute 37 fordelivering combustible material to the feed opening 14 of body 11 tocharge the same. A chute extension for directing flow of the wastematerials through enclosure 10 to feed opening 14 is also omitted fromthe drawing.

Attention is now invited to FIGS. 2-8 for a more detailed discussion ofthe construction of hollow body 1 1, its grates and grate supportingmeans therein. Referring to the right half of FIG. 3, one may see thatthe conical portion of hollow body 1 1 is comprised of a plurality ofoffset struts illustrative ones of which are marked 45-52. As is thecase with all the struts, the upper ends 53 and 54 of typical struts 48and 49 are welded to a flange ring 55 as are the corresponding upperends of adjacent struts. The lower ends 56 and 57, for example, ofstruts 48 and 49 are welded to a relatively smaller diameter flat ringor apertured flange 16. As can be seen in FIG. 4, flange 16 has severalcircumferentially spaced holes 58 for bolting the flange and housing 12to turntable 13 as shown in FIG. 1. The various struts, which aredisposed in a circular pattern, are offset in their central region andabut each other as indicated in the vicinity of reference numeral 59.These butt joints are preferably welded. Thus, one may see that fourquadrants formed of struts such as 45-52 will define a conical hollowbody portion wherein the inside edges of all of the struts define a coneof revolution. Viewed from the outside, the struts present theappearance of a lattice structure.

One portion of hollow body 11 is substantially cylindrical as designatedgenerally by the reference numeral 60. The axial boundaries ofcylindrical portion 60 are defined by intermediate flange 55 and an endflange 61 to which shroud 15 is attached by any suitable means. Anotherlattice structure defining cylindrical portion 60 of hollow body 11 isformed with struts such as 62-67 which are arranged in triangularrelationship and have their opposed ends welded respectively to flanges55 and 61. The manner of welding struts such as 65 and 66 in thecylindrical portion of the body and struts 53 and 54 in the conicalportion with flange 55 is exhibited in FIG. 5.

It will be evident to those skilled in the art that the offsets or bendsin the central regions of the juxtaposed struts which form the conicalportion of body 1 1 being in abutment with each other at points such as59 result in a rigid, lightweight lattice structure which is adapted toexpand or extend axially and radially to a limited degree foraccommodating thermal and other physical stresses exerted in anydirection. The triangularly disposed struts such as 62-67 impart similarproperties to the cylindrical portion 60 of hollow body 11.

One may see in the left portion of FIG. 3 that triangularly arrangedstruts such as 62-67 present straight edges to the interior of hollowbody 11 to define an interior cylinder of revolution. The inside surfaceof this cylinder is marked with the numeral 68 in FIGS. 2 and 3.Similarly, offset'struts such as 45-52 present straight edges to theinterior of hollow body 11 which define a cone of revolution that ismarked with the numeral 69. This can also be clearly seen in FIGS. 2 and3.

FIGS. 2 and 3 show that within cylindrical portion 60 of body 11 arecircumferentially spaced clips such as intermediate clip 70 and axiallyspaced apart clips 71 and 72 which are welded to the individualtriangularly arranged struts. Intermediate clip 70 is provided with aslot 73, as are other corresponding clips, for accommodating gratesupport ring 74. Similarly, clips 71 and 72 are slotted for receivinggrate support rings 75 and 76, respectively.

One type of grate which may be supported on the set of rings 74-76 isdepicted in FIGS. 6 and 7. The grates 12 are shown in phantom in FIG. 2.These grates are disposed adjacent each other around the interior ofcylindrical body portion 60 as can be seen particularly well in FIG. 1.

In the type of the grate shown in FIGS. 6 and 7, one edge has anL-shaped slot 77 which constitutes a hook so that the center of theelongated grate 12 may be engaged with an intermediate grate supportring such as 74. Note that the edges of the grates at their end portions78 and 79 are planar and that their sides have a plurality of grooves 80so that when the grates are sideby-side there will be radial openingsfor air to pass into hollow body 11 and for fine ashes to fall out. Frominspection of FIG. 2, it will be evident that the juxtaposed grates 12are hooked on intermediate support ring 74 and that their opposed planarend portions 78 and 79 merely bear on axially spaced apart support rings75 and 76. Thus there is only one point of engagement between each grate12 and an intermediate support ring 74 while the end portions of thegrates are free to expand and contract and have no restraints.

The conical part of hollow body 11 has three rows of grates 12encircling the interior of the body as can be seen in FIGS. 1-3. Thegrates 12 in the top row within the conical portion are all supported onan intermediate support ring 90 and their opposed ends bear freely onopposite axially spaced apart support rings 91 and 92. Support rings90-92 are retained by clips 93-95,

- respectively, which are welded to the lattice struts. Axiallydisplaced rows or grates 12 are similarly releasably supported onintermediate rings 96 and 97. There are a pair of axially spaced apartgrate end supporting rings 98 and 99 cooperating to support a row ofgrates with intermediate ring 96 and there are another pair of spacedapart support rings 100 and 101 cooperating with intermediate ring 97 tosupport the lowermost row of grate bars 12 which encircles the interiorof the conical portion of hollow body 11. All of the support rings arecaptured in slotted retaining clips such as 94 and 95. The rows ofgrates 12 encircling the interior of hollow body 11 define a combustionspace for materials fed in through feed opening 14 of hollow body 11. Asthe hollow body rotates in the assembly depicted in FIG. 1, ash andother fine particles sift through the opening defined by grooves 80 inthe grates, and these fine materials accumulate in the bottom ofenclosure from which they are periodically removed by opening a door inthe ash hopper, not shown. Large noncombustible pieces which areinevitably found in waste materials are periodically removed from thecombustion chamber in hollow body 11 through an opening 105 in bottomflange 16, as can be seen in FIG. 2. As mentioned earlier, the means forclosing opening 105 during operation of the incinerator may be aconvexly shaped valve, not shown, which is advanced and retracted byhandwheel 18 outside of the incinerator mechanism as can be seen in FIG.1.

Another type of grate bar 12 is depicted in the side and plan views ofFIGS. 8 and 9 respectively. Grate bars of the 12' type may be considereda preferred form. They are so shaped that when they are arranged in rowsin the conical support there is more space for ashes and small particleswhich are usually completely burned to drop into the ash hopper. Thesebars also allow anchoring them to the intermediate supporting ringspositively with a pin without inhibiting thermal expansion andcontraction.

In FIGS. 8 and 9 a typical grate bar 12' comprises an elongate oraxially extending body or web whose sides 111 and 112 are slightlybeveled or converging toward each other. Integral with opposite ends ofbody 110 are substantially T-shaped heads 113 and 114, the latter beingnarrower than the former in a direction transverse to the elongated body110. A foot 115 extends down from heat 113 and a foot 1 16 extends fromhead 114. The bottom surfaces 118 and 119 respectively of the feet areflat and adapted to rest on the axially spaced apart support rings suchas rings 98 and 99 of cone 11 in FIG. 3.

Extending downwardly from body 110, as can be seen clearly in FIG. 8,are a pair of tongues 120 and 121 which define a slot 122 by which thegrate bar 12' may be engaged with a support ring 96, in FIG. 3, whichring is axially intermediate rings 98 and 99 in this figure. A crosssection of a typical intermediate support ring is shown in phantom inFIG. 8. The tongues have aligned holes 123 for receiving a pin, notshown, for loosely but positively securingeach grate bar 12' to itsintermediate supporting ring. Ribs 124 and 125 between the heads 113 and114 and tongues 120 and 121 serve as reinforcement for the tongues.

The overall longitudinally beveled or tapered shape of the grate bars12' permits them to be positioned next to each other with the sides oftheir T-heads 113 and 114 abutting regardless of the fact that theaxially spaced supporting rings have different diameters due to theconical shape of part of the support structure 11.

The invention is not limited to the embodiments shown in the drawings.For instance, hollow body 11 of the grate structure may have othershapes such as a basket, bulb or sphere. However, the partially conicaland partially cylindrical type described has the advantage of inducingconstant agitation and demixing in the combustion chamber and so'promotes more complete combustion of the wastes.

In summary, a new rotating grate structure for an incinerator or othertype of furnace has been described. The grate structure is distinguishedby using a hollow supporting frame which has a cylindrical portion andan axially contiguous conical portion which are both comprised of strutsthat form a lattice. The internal rows of grates are releasably engagedwith concentric and axially spaced apart intermediate support means.

The ends of the grates merely rest on support ring means which are onopposite sides of each of the intermediate rings. The lack of axialrestraint on the end portions of the grates permit them to expand andcontract and otherwise yield so that they do not develop internalstresses or torsional forces that might cause the grates to fracture asin prior art designs.

Although a preferred embodiment of the invention has been described indetail, such description is to be considered illustrative rather thanlimiting, for the invention may be variously embodied and is to belimited only by interpretation of the claims which follow.

I claim:

1. in a pyrometric incinerator for disposing of com bustible waste andthe like, grate structure comprising:

a. a rotatably mounted hollow body means having a feed opening,

b. axially spaced apart grate support means mounted interiorly of saidbody means and extending generally circumferentially therein, one ofsaid support means being axially intermediate other of said supportmeans,

c. elongated grate bar means disposed adjacent each other about theinterior of said body means and extending generally axially to define acombustion chamber,

d. said grate bar means having opposite end portions and an intermediateportion, the intermediate portion of said grate bar means having slotmeans for detachably engaging said grate bar means with saidintermediate support means and said opposite end portions beingsupported in an axially unrestrained manner on said other support meansrespectively.

2. The invention set forth in claim 1 wherein:

a. the opposite end portions of said grate means are planar and bearslidably on said other support means.

3. The invention set forth in claim 1 wherein:

a. said grate support means comprise ring means which are axiallydisplaced from each other and substantially encircle the interior ofsaid hollow body means,

b. said intermediate portion of the grate means being releasably engagedwith said intermediate ring means and said opposite end portions bearingon said other of said ring means.

4. The invention set forth in claim 3 including:

a. a plurality of circumferentially spaced apart ringretaining means foreach of said ring means, said retaining means being fastened to theinterior of said body means.

5. The invention set forth in claim 1 wherein:

a. said body means comprises a substantially conical hollow portion anda contiguous coaxial cylindrical hollow portion, some of saidintermediate and said other support means being mounted in said conicalportion and other of said intermediate and said other support meansbeing mounted in said cylin- LII drical portion.

6. The invention set forth in claim 1 wherein:

a. said hollow body means comprises axially spaced apart flange meanswhich each have an opening, b. a plurality of circumferentially adjacentstrut means extending in a generally axial direction and having theiropposite corresponding ends fastened to the flange means, respectively.

7. The invention set forth in claim 6 wherein:

a. certain of said strut means are offset intermediate their ends in onecircumferential direction and other of said adjacent strut means areoffset intermediate their ends in an opposite circumferential directionand in contact with said certain strut means, whereby the strut meansmutually support each other.

8. The invention set forth in claim 6 wherein:

a. adjacent pairs of strut means diverge from their corresponding endswhich are fastened to one flange means so as to contact next adjacentpairs of said strut means and then converge to their other correspondingends which are fastened to the other of said flange means.

9. For use in an incinerator, a hollow grate support body comprising:

a. a truncated conically shaped lattice means having an opening at oneaxial end and a relatively smaller opening at it other end, and

b. grate supporting means mounted on the substantially conical interiorof said lattice means.

10. The invention set forth in claim 9 including:

a. a substantially cylindrical lattice means axially adjacent and fixedto said conically shaped lattice means.

11. The invention set forth in claim 9 wherein:

a. said conically shaped lattice means comprises axially spaced apartflange means, and

b. strut means distributed circumferentially about the exterior of saidhollow body and fastened at opposed ends to respective flange means.

12. The invention set forth in claim 11 wherein:

a. said strut means extend generally in an axial direction between saidflange means, at least some of the strut means being offset andcontacting adjacent strut means.

13. The invention set forth in claim 10 including:

a. axially spaced apart flange means at opposite ends of saidcylindrical lattice means, and

b. strut means extending between and fastened to said last-named flangemeans defining said lattice means.

14. The invention set forth in claim 13 wherein:

a. said strut means are arranged in triangular fashion circumferentiallyof said body to define said lattice means.

1. In a pyrometric incinerator for disposing of combustible waste andthe like, grate structure comprising: a. a rotatably mounted hollow bodymeans having a feed opening, b. axially spaced apart grate support meansmounted interiorly of said body means and extending generallycircumferentially therein, one of said support means being axiallyintermediate other of said support means, c. elongated grate bar meansdisposed adjacent each other about the interior of said body means andextending generally axially to define a combustion chamber, d. saidgrate bar means having opposite end portions and an intermediateportion, the intermediate portion of said grate bar means having slotmeans for detachably engaging said grate bar means with saidintermediate support means and said opposite end portions beingsupported in an axially unrestrained manner on said other support meansrespectively.
 2. The invention set forth in claim 1 wherein: a. theopposite end portions of said grate means are planar and bear slidablyon said other support means.
 3. The invention set forth in claim 1wherein: a. said grate support means comprise ring means which areaxially displaced from each other and substantially encircle theinterior of said hollow body means, b. said intermediate portion of thegrate means being releasably engaged with said intermediate ring meansand said opposite end portions bearing on said other of said ring means.4. The invention set forth in claim 3 including: a. a plurality ofcircumferentially spaced apart ring-retaining means for each of saidring means, said retaining means being fastened to the interior of saidbody means.
 5. The invention set forth in claim 1 wherein: a. said boDymeans comprises a substantially conical hollow portion and a contiguouscoaxial cylindrical hollow portion, some of said intermediate and saidother support means being mounted in said conical portion and other ofsaid intermediate and said other support means being mounted in saidcylindrical portion.
 6. The invention set forth in claim 1 wherein: a.said hollow body means comprises axially spaced apart flange means whicheach have an opening, b. a plurality of circumferentially adjacent strutmeans extending in a generally axial direction and having their oppositecorresponding ends fastened to the flange means, respectively.
 7. Theinvention set forth in claim 6 wherein: a. certain of said strut meansare offset intermediate their ends in one circumferential direction andother of said adjacent strut means are offset intermediate their ends inan opposite circumferential direction and in contact with said certainstrut means, whereby the strut means mutually support each other.
 8. Theinvention set forth in claim 6 wherein: a. adjacent pairs of strut meansdiverge from their corresponding ends which are fastened to one flangemeans so as to contact next adjacent pairs of said strut means and thenconverge to their other corresponding ends which are fastened to theother of said flange means.
 9. For use in an incinerator, a hollow gratesupport body comprising: a. a truncated conically shaped lattice meanshaving an opening at one axial end and a relatively smaller opening atit other end, and b. grate supporting means mounted on the substantiallyconical interior of said lattice means.
 10. The invention set forth inclaim 9 including: a. a substantially cylindrical lattice means axiallyadjacent and fixed to said conically shaped lattice means.
 11. Theinvention set forth in claim 9 wherein: a. said conically shaped latticemeans comprises axially spaced apart flange means, and b. strut meansdistributed circumferentially about the exterior of said hollow body andfastened at opposed ends to respective flange means.
 12. The inventionset forth in claim 11 wherein: a. said strut means extend generally inan axial direction between said flange means, at least some of the strutmeans being offset and contacting adjacent strut means.
 13. Theinvention set forth in claim 10 including: a. axially spaced apartflange means at opposite ends of said cylindrical lattice means, and b.strut means extending between and fastened to said last-named flangemeans defining said lattice means.
 14. The invention set forth in claim13 wherein: a. said strut means are arranged in triangular fashioncircumferentially of said body to define said lattice means.